The present invention relates generally to a method and apparatus for determining the presence of voltage and determining the phase relationship between capacitive test points. More specifically, the present invention is directed to determining the presence of voltage at capacitive test points and measuring the actual phase angle difference between the two capacitive test points in order to determine the phase relationship between the two capacitive test points.
In the past, the phase relationship between two capacitive test points was determined based on voltage measurements at the capacitive test points. Ideally, the voltage difference between the two capacitive test points would be zero if in phase and significantly larger if out of phase. However, due to the fact that the test point capacitive divider ratio can vary significantly from one test point to another, a large voltage difference between the two capacitive test points could occur due to the capacitive divider ratio difference and not due to the phase angle difference between the two capacitive test points. Therefore, the wrong conclusion could be reached regarding the phase relationship between the two capacitive test points. Moreover the prior art devices used to measure the phase relationship have a very high input impedance, which makes these devices very sensitive to contamination on the capacitive test point insulation surface, thus, giving an inaccurate voltage reading at the capacitive test points.
In general, the capacitive test point systems operate in the range of 15 KV (kilovolts) to 35 kV (kilovolts). In the past, the devices used for measuring the voltage and phase angle relationships between the two capacitive test points are often known to indicate no presence of voltage at the capacitive test points due to factors such as contamination at the capacitive test point insulation surface and any defects in the capacitive test point system itself.
Thus, a need exists to detect the phase relationship between capactive test points independent of the capacitive divider ratio difference and the capacitive test point voltage accuracy. Also, there is a need for a capacitive test point voltage and phasing detector with a very low input impedance and also capable of accurately detecting the presence of voltage in the capacitive test points independent of the voltage range in the systems, independent of any contamination or defects that may occur in the systems.
It is an object of the present invention to provide an apparatus and method of detecting the phase relationship between the capacitive test points which is completely independent of both the capacitive divider ratio variations and the capacitive test point voltage accuracy. The present invention provides a capacitive test point voltage and phasing detector which determines the phase relationship between two capacitive test points based on the actual phase angle difference between the two capacitive test points. A voltage waveform, that is, a signal is received at each capacitive test point. The actual phase angle difference is determined based on any phase shift between the two voltage waveforms, independent of the actual voltage difference between the two capacitive test points.
It is a further object of the present invention to provide an apparatus and method of ensuring that both the capacitive test points are energized indicating that the voltage is present at both the capacitive test points. This protects the possibility of errors occurring if both the points are not energized. In other words, the present invention provides a capacitive test point voltage and phasing detector which determines the presence of voltage at both the capacitive test points, which prevents it from providing an indication that the voltages are in or out of phase unless both the capacitive points are energized. This further eliminates any possibility of errors that might occur in determining the phase angle relationship between the two capacitive test points.
It is another object of the present invention to provide a capacitive test point voltage and phasing detector which has a very low input impedance minimizing the effects of contamination on the capacitive test point insulation surface. Thus, giving an even more reliable reading of the phase angle relationship between the two capacitive test points.
It is still a further object of the present invention to provide a capacitive test point voltage and phasing detector which is capable of accurately detecting the presence of voltage in the capacitive test points independent of the voltage range in the systems, independent of any contamination or defects that may occur in the capacitive test point systems.